Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 6500 | Thousand metric tons | NA |
| 2004 | 6500 | Thousand metric tons | 0.00% |
| 2005 | 6500 | Thousand metric tons | 0.00% |
| 2006 | 6500 | Thousand metric tons | 0.00% |
| 2007 | 6200 | Thousand metric tons | -4.62% |
| 2008 | 6000 | Thousand metric tons | -3.23% |
| 2009 | 5500 | Thousand metric tons | -8.33% |
